Antenna array



R. E. PLUMMER ANTENNA ARRAY Oct. 29, 1963- 2 Sheets-Sheet 1 Filed Nov.2, 1959 ROBERT E. PLUMME INVENT ATTORNEY Oct. 29, 1963 R. E. PLUMMER 3,7

ANTENNA ARRAY Filed NOV. 3, 1959 2 Sheets-Sheet 2 URRENT SUPPLY ROBERTE. PLUMMER.

INVENTOR g; I; ATTORNEY United States Patent poration of Delaware FiledNov. 2, less, Ser. No. 851,212 6 Qlaims. ((Il. S ilt-1%) The presentinvention relates to antennas and more particularly to means forelectronically controlling the disection and shape of a beam ofelectromagnetic energy radiated from an antenna array.

In the past, it has been customary for radar systems to employ antennameans wherein the shape of the radiated beam is determined by thephysical shape of the structure while the direction of the beam isdetermined by the physical position of the antenna. In order to obtainthe desired amount of beam shaping it has been necessary for the antennaarray to be large and bulky. This results in the antenna array havinglarge inertia which in turn imposes limits on the speed at which thearray can be moved. In addition, the array is subject to large forceswhenever it is exposed to a high wind.

These and other problems are particularly acute in airborne radarwherein the antenna array is mounted on an aircraft. A partial solutionto these problems is to place the antenna array inside of a streamlinedradome mounted on the aircraft. Although these radomes are more or lesstransparent to electromagnetic radiations, they may cause distortions ofthe beam and/ or they project from the surface of the aircraft andthereby produce an objectionable amount of aerodynamic drag.

More recently, numerous eiforts have been made to develop antenna meansthat may be mounted flush with the exterior surface of the aircraft. Inone form of flush mounted antenna array a waveguide system is providedthat has a plurality of radiating apertures disposed in the surface ofthe aircraft. This type of antenna eliminates the necessity for a radomeand also decreases the aerodynamic drag. The control over the radiationpatterns from these antennas heretofore has not been entirelysatlisfactory and also it has been extremely difli cult, if notimpossible, to vary the direction of the radiated electromagnetic beamthroughout a sufiiciently wide area.

:It is therefore an object of the present invention to provide anantenna array having electronic means for controlling the shape of theradiation pattern.

It is also an object to provide an antenna in which the beam ofelectromagnetic energy may be electronically scanned throughout anydesired angle at a high rate of speed.

It is also an object to provide means for readily controlling the shapeof the radiation pattern of an antenna array.

These and other objects are to be accomplished by providing an antennaarray which includes at least one waveguide having a plurality ofradiation apertures in one wall thereof adapted to be excited by atraveling wave of electromagnetic energy within the waveguide. Thedegree of coupling of each aperture to the traveling wave isindividually controllable by separate field rotating means for eachaperture. The traveling wave is fed into the waveguide in a mode thatwill not excite the apertures but the field rotating means will beeffective to convert at least a portion of the energy into a mode thatwill excite the apertures subsequent thereto. Thus it is possible toseparately control the amount of coupling between each individualaperture and the traveling wave. This in turn allows the amounts ofradiation from each of the apertures to be controlled whereby the shapeof the radiation pattern may be controlled.

319E. i Patented Get. 29, 1963 In addition, separate phase shiftingmeans may be provided, for each of the individual apertures whereby thephases of the individual radiations may be controlled. This in turn willpermit the direction of the resultant beam of electromagnetic energy tobe varied throughout any desired range.

-In the drawings:

FIGURE 1 is a perspective view, with portions thereof broken away, of anantenna array embodying one form of the present invention.

FIGURE 2 is a plan view of an antenna array embodying a modification ofthe present invention.

FIGURE 3 is a perspective view of control means for the antenna array inFIGURE 2.

Referring to the drawings in more detail, the present invention isembodied in an antenna array 10 for radiating a beam of electromagneticenergy into space. The array includes a plurality of waveguides that areadapted to be connected to one or more sources of electromagneticenergy. (not shown). In the present instance there are only twosubstantially identical waveguides l2 and 14 illustrated; however, itwill become apparent that only a single waveguide or a large number ofwaveguides ma be employed, if desired The first waveguide 12 is of theso-called square type in which the corresponding dimensions of each ofthe side walls 24, 26, 28 and 30 are substantially identical. As aresult, the waveguide 12 is capable of conducting a traveling wave ofelectromagnetic energy with equal facility in either of two fundamentalmodes. For example, a traveling wave of energy may be propagated alongthe waveguide 12 in the TE and/or the TE modes. The electric fields ofthese modes are indicated by the arrows E and E respectively in FIG. 1.

The input end 16 of the waveguide 12 is adapted to be coupled to asource of microwave energy of desired frequency whereby a traveling waveof electromagnetic energy will be propagated along the waveguide 12.This source which is not shown may be of any conventional design but ispreferably interconnected with the Waveguide 12 for creating a travelingwave in the waveguide that will be propagated along the guide 12entirely in the TE mode.

The opposite end 20 of the waveguide is terminated in a power absorbingload. Thus, any energy that reaches this end will be absorbed and willnot be reflected backwardly along the waveguide.

A plurality of apertures are provided in one of the side walls 3% of thewaveguide 12 for coupling the electromagnetic energy in the travelingwave from the inside of the waveguide 12 to the outside of the waveguide12. Although the apertures may be any desired variety, in the presentinstance they comprise a series of substantially identical elongatedslotsrsuch as slot 32D that are located in the center of the side wall30.

The slots 32 are relatively narrow but of resonant length with the longdimension extending substantially parallel to the axis of the waveguide12. It may be seen that the currents induced in the side wall 3% by theTE mode will not intersect any of the slots, and accordingly, theseslots will be inefiective to couple any of the energy in the TE mode tothe exterior of the waveguide 12.

However, energy being propagated along the waveguide in the TE mode willcreate currents in the side wall 30 that will excite the slots. As aconsequence, it may be seen that at least a portion of the energy in theTE mode present at any given slot will be coupled to the exterior of thewaveguide 12.

In order to separately control the individual amounts of couplingbetween each of the slots 32 and the traveling wave in waveguide 12, afield rotating means 34A to U 34G is provided anterior to each of theslots 32 for rotating the field of the traveling wave. In addition,field rotating means 34H may be provided posterior to the slot 32G.

In the present instance, these field rotating means utilize theso-called Faraday field rotating efiect wherein the presence of aferrite and a magnetic field will cause the electric field to undergoangular rotation as it progresses therethrough. The field rotating means34 are all substantially identical and include coils 36A to 366 wrappedaround the exterior of the waveguide 12. Thus a direct current in one ofthese coils will create a DC. magnetic field inside of the waveguide. Inaddition, a ferrite core 38 is provided in the center of the waveguide12 so as to be disposed in this field. The core 33 may be a singlemember that forms a continuous cylinder of ferrite mate rial thatextends the entire length of the waveguide 12. However, if desired, thecore may comprise separate sections of ferrite that have lengthscorresponding to the lengths of the coils and are positioned inalignment with the coils 36. Thus the ferrite material will not extendinto the vicinity of the slots and the slots will be isolated from theeffects of the magnetic field. Nonferrite sections having the samedielectric constant as the ferrite sections may be provided between theferrite sections and in alignment with the slots 32 to preventundesirable reflections of energy within the waveguide.

It may be seen that the application of a direct current to anyparticular coil 36A to 36H will cause a D.C. flux field in the waveguideand in the ferrite core that will cause the field of the traveling waveto rotate as the energy in the wave passes through the coil. Thedirection and amount of this rotation will be a function of thedirection and amount of the current in the coil, respectively. As thefield of the wave rotates the mode of propagation of the wave will tendto change from the T E mode to the TE mode or vice versa. Ninety degreesof rotation will cause the waves propagation to be completely changedfrom one mode to another. However, a lesser amount of rotation willcause the traveling wave to have one component thereof propagated in theTE mode and another component thereof propagated in the TE mode.

If the energy is introduced into the waveguide 12 entirely in the TBmode, the field of the wave will be oriented as indicated by the arrow Eand as the energy travels along the guide there will be no couplingbetween the traveling wave and the slots 32. However, if a directcurrent of some predetermined amount is circulating in one of the coils,for example 36D, the field of the traveling wave will rotate by somepredetermined amount less than ninety degrees as it passes through thefield of coil 36D. Thus, the traveling wave posterior to the energizedcoil 36D will include two separate components, one of which will be inthe TE mode and the other of which will be in the TE mode. Thus at leastthe first .slot 32D subsequent to the energized coil 36D will be excitedby the traveling wave inside of the waveguide and at least a portion ofthe energy in this mode will be coupled to the outside of the guide 12.The amount of energy passing through the slot 32D will be a function ofthe amplitude of the component in the TE mode which in turn will be afunction of the current in the coil 36D.

If it is desired to excite one or more of the succeeding slots such as32E, 32F, and/or 326 to the same or different extents, the coils 36E,36F, and/or 36G immediately anterior to slots 32E, 32F, and/or 32G,respectively, may be energized by a direct current. The amplitude ofthis current may be chosen so as to rotate the field of the travelingwave just suificiently to produce a component in the TE mode with anamplitude requisite for producing the desired degree of excitation ofthe slots 32E, 32F and/ or 32G.

If it is desired to prevent one or more of the succeeding slots 32E, 32Fand/ or 320 from being coupled to the traveling wave, a current ofreversed polarity may be circulated through coil 36E, 36F, or 36G. Thiswill cause the traveling wave field to be rotated back into the TE mode.Thus all of the energy in the traveling wave reaching the slotssubsequent to the reversely energized coil 36E, 36F or 36G will be in amode that will not excite the slots. Consequently, no electromagneticenergy will pass through any of these slots. It may thus be seen thatthe slots that are excited and the amount of excitation thereof may beindividually and independently controlled by the current in the coils36A to 36G. The coil 36H may be utilized to insure the energy arrivingat the end 20 being entirely in the TE mode. Thus in the event anyenergy is reflected back along the waveguide, it will not excite theslots.

If the slots 32 were free to radiate the energy passing therethroughdirectly into space, the resultant radiations would combine with eachother to form a beam of energy whereby the waveguide 12 would act as anantenna. The direction of the beam would be determined by variousfactors such as the size and spacing of the slots, the relative phasesof the radiations, etc. Normally, the direction of the beam would befixed relative to the waveguide and would be directed obliquely to theaxis of the waveguide, i.e., the structure would act as somethingbetween an endfire array and a broadside array.

The shape of the radiation pattern will be determined by the number ofslots that are excited and the relative amplitudes of the radiationsfrom the slots 32. Accordingly, varying the amounts of the currentsflowing through the various coils 36 will vary the radiation pattern.With a single waveguide such as 12 it would be possible to produce beamsharpening in planes containing the axis of the waveguide 12 and/ or theslots 32.

Although it would be possible to permit the slots to radiate directlyinto space and thereby act as an antenna array it has been foundpreferable to employ a separate auxiliary waveguide 33A to 38G for eachslot 32A to 326 (only 32D shown). The auxiliary waveguides 38 are allsubstantially identical and have a rectangular cross section and are ofrelatively short length. Each guide 38 is rigidly secured to the mainwaveguide 12. whereby one end of the guide registers with a slot. Thebroad walls of the guides 38 are all parallel to the long dimensions ofthe slots 32 so that the open ends or apertures 42A to 42G of the guides38 form a straight row. Thus, any energy passing. through a slot 32 willtravel along one of the auxiliary waveguides 3S and be radiated intospace from the open end 42 thereof.

Each auxiliary waveguide includes a phase shifter for controlling thephases of the radiations from the apertures 42. Each phase shifterincludes a coil 44A to 446 that is wound around the exterior of theauxiliary guide and a ferrite core 46A to 46G (only 46D shown) that isinside of the auxiliary guide. The core 46 may be either ferrite stripson the top and bottom broad walls of the guide to produce a negativephase shift or a ferrite rod in the center of the guide to produce apositive phase shift.

The current in a particular coil 44 will produce a DC. magnetic field inthe waveguide and in the core. Since the auxiliarywaveguides are ofrectangular shape, this will be effective to control the phase of anyenergy that is traveling through the waveguide 40. Thus the individualradiations emanating from each of the open ends 42 of the auxiliaryguides 38 may be readily controlled by means of the current flowingthrough the coils 44.

It may be seen that varying the current flowing through the coils 36 inthe field rotating means will control the amount of coupling between theslots 32 and the energy in the traveling wave. Thus the current in thecoils will therefore be effective to determine the amount of beamsharpening in planes containing the apertures 42. Also it is apparentthat varying the currents flowing through the coils 44 in the phaseshifting means will vary the relative phase of the radiations emanatingfrom the apertures ergized with predetermined amounts of current.

42 and will therefore be eflective to determine the direction of thebeam.

If it is desired to provide additional control over the shape anddirection of the beam, additional waveguides such as waveguide 14 may beprovided. In the present instance, only one additional guide is shown,but it will be apparent that if more complete control is required agreater number of waveguides may be employed.

The waveguide 14 is substantially identical to the first waveguide 12 inthat it is also of square dimension and can carry electromagnetic energyin either the TB mode or in theTE mode. The input end 18 of thewaveguide 14 may be connected to the same source of energy as the firstwaveguide 12. The energy is fed into the wave so that it will bepropagated along the guide in the TE mode. One side wall of thewaveguide 14 has a row of slots 48 therein that are substantially thesame as in the first waveguide 14. The long dimensions of the slotsextend parallel to the slots 32 in the first waveguide 12 and to theaxis of the second waveguide 14. As a consequence, the slots will not beexcited by any of the energy in the T E mode, but they will be excitedby the energy in the TE mode.

A separate field rotating means 56 is provided for each of the slots 48Ato 486 (only 48A shown) and one is provided posterior to all of theslots d8. These means may be substantially identical to those in thefirst waveguide and include a ferrite core 52 in the center of thewaveguide 14 and coils 54 wound around the exterior of the waveguide 14.These coils 54 and core 52 will thus be efiective to control the amountof energy that is coupled out of the waveguide 14 at each slot 4-8.

In addition, separate auxiliary waveguides 56 are provided for each slot48. These waveguides 56 are substantially identical to those in thefirst waveguide and the ends thereof form a second row of radiatingapertures 58 that is parallel to the first row. Each auxiliary waveguideis provided with phase shifting means that includes a coil 6th on theoutside of the waveguide 56A and a ferrite core 62A in the center. thesecoils 60 are effective to control the phase relations of the energiesemanating from the apertures 58.

In order to employ the antenna array 10 for scanning an area with a beamof radiated electromagnetic energy, a source of microwave energy isenergized to supply microwave energy to the input ends 16, 18 of thewaveguides 12, 14. This energy will then be propagated along thewaveguides l2 and 14 by means of traveling waves that are in the TEmodes. The energy in this mode will be ineffective to excite any of theslots, and accordingly, there will be no coupling of such energy to theoutside of either of the waveguides.

In order to cause radiations of a beam of electromagnetic energy fromthe antenna array, preselected combinations of the field rotating coils35A to 36G are en- As the energy in the traveling waves passes throughthe coils and along the core the electric fields will be rotated. As aresult, a component of energy in the TE mode will be present at each ofthe slots 32, 43 that it is desired to excite. The intensities of theexcitations of the slots 32 in the first waveguide 12 relative to eachother and the intensities of the excitations of the slots 48 in thesecond waveguide 14 relative to each other will be effective to controlthe amount of beam sharpening in planes containing the apertures'42, 58.The intensities of the excitations radiated from apertures 42 relativeto those radiated from the apertures 58 will be effective to control theamount of beam sharpening in planes normal to the side wall 26. It maythus be seen that by controlling the current in the coils 36 and 54, theradiations from the apertures 42 and 58 may be collimated or focusedinto a pencil beam or into any other desired shape.

In addition, the control means may be effective to vary the current inthe phase coils 44- and 60. Thus the phases of the radiations from theapertures 42A to 42G relative The currents flowing through 6 to eachother may be varied so as to control the direction of the beam in planescontaining the apertures 42. Also, the currents in the coils 66 may bevaried relative to each other to control the direction of the beam inthe same planes.

In addition, the currents in the coils 44 may be adjusted relative tothe currents in the coils 64) so as to regulate the relative phaserelationship between the radiations from the two rows of apertures so asto control the direction of the beam in planes normal tothe side Wall26.

It will thus be seen that it is possible to focus the beam bycontrolling the currents in coils 36 and 54- and to control thedirection of the. beam by varying the current in coils 44 and 60'. As aresult, the beam may be scanned throughout an area. by electronic means,thus eliminating the necessity for any mechanical movement or" theditierent. portions of the antenna array.

In order to provide a control for these coils a current supply may beconnected to commutating means such as slip. rings and brushes. Thiswill energize the field rotating coils in a certain sector so that theenergy in the traveling wave will be coupled to the auxiliary guides inthis sector and will be radiated from the open ends of these guides.

In order to collimate these radiations the commutating means may alsoenergize the phase shifting means on the radiating auxiliary guides soas to produce a phase shifting of the radiated signals. Thus, theelevation of the beam may be controlled by means of the phase shiftingcoils. If it is desired to focus the beam more sharply, a plurality ofthe circular arrays may be provided.

If it is desired to sweep the electromagnetic beam throughout a greatervolume, the array 16d in FIGURES 2 and 3 may be employed. In thisembodiment the antenna array includes a plurality of waveguides that areformed into substantially complete circles and are stacked up on top ofeach other so as to be substantially normal to the axis of the array.The input ends 164 of the waveguides are disposed immediately adjacentthe terminal ends 136 and are adapted to receive electromagnetic energyfrom a waveguide 168 that is connected to an energy source.

Each of the waveguides 162 has a substantially square cross section sothat a traveling wave of electromagnetic energy may be propagatedtherealong in either of two fundamental modes, for example, the TE modeor the TE mode.

The waveguide 103- is connected to the input end 104 so that a travelingwave of energy will be launched into and propagated along the guide 192entirely in the TE mode. The terminal end 196 of the guide 102 isprovided with a nonreflecting load that will absorb any energy that mayreach that end.

The outer cylindrical walls of the waveguides 102 include a plurality ofapertures that are adapted to couple the energy in the traveling wavefrom the inside to the outside of the waveguide 10-2. In the presentinstance, these apertures comprise elongated slots having a resonantlength with the long dimensions thereof extending in a circumferentialdirection.

Thus, any energy in the TE mode which is present in the waveguides willnot set up any currents in the side walls 11d that will excite theslots. Consequently, energy in such a mode will not be coupled throughthe slots to the outside of the waveguide 102.

In order to separately control the individual degrees of couplingbetween the various slots and the energy in the traveling waves, aseparate field rotating means is provided immediately anterior to eachslot. These field rotating means are substantially identical to those inthe first embodiment. Each field rotating means includes a coil 112 thatis wound around the exterior of the waveguide 192 and a ferrite core 114that is disposed in the center thereof. For the sake of clarity only oneof these coils 7 112 is shown in the drawings, but it should beunderstood that there are separate coils for each slot.

The ferrite core 114 may be a substantially continuous ring of ferriteor a plurality of ferrite sections aligned with the coils and nonferritesections aligned with the slots.

The currents in the coils 112 are regulated by a control means 116 whichincludes a current source that has a plurality of separate outputs 118,120, 122, 124 and 126'. Each output is adapted to supply a predeterminedamount of direct current that may be of the same amount or a diiferentamount than that in the other outputs. Each output is connected to aseparate slip ring 128, 130, 132, 134 and 136. These rings are fixed,i.e., they remain in a stationary position.

A rotating commutator 138 is provided that has a plurality of separatesegments 149 that correspond in number to the number of coils 112 on thewaveguide 1 2. A preselected group of these segments 14% are grounded at14-2 while another group are connected to brushes 144 that slide on theslip rings. Each of the coils 112 is connected to one or more brushes145 that ride on the surface of the commutator 13S and successivelycontact the various segments 14%. It may thus be seen that as thecommutator 13% rotates, the coils 112 will be energized in sequence andthe currents in the coils 112 will be equal to predetermined amountsthat are determined by currents from the outputs 118 to 126.

Since the currents in the coils 112 determine the amount of energy thatis coupled out through the slots, there will be energy coupled out insequence so as to produce a beam that will rotate about the axis of thearray The number of slots in each waveguide 102 that are excited and therelative amplitudes of the excitation will be effective to determine theamount of collimation of the radiations and thus will provide a controlover the focusing of the beam.

In addition, a separate auxiliary waveguide 146 is provided on theexterior of each circular waveguide 192 for each slot. The inner ends ofthe auxiliary waveguides 145 are secured to the waveguide 102 so as toregister with the slots and so as to project radially outward. Thewaveguides 146 are preferably of rectangular cross sections with thewide dimensions running parallel to the lengths of the slot. Thus theouter or open ends of the auxiliary waveguides 146 for each of thewaveguides 102 will form a circle of radiating apertures. It may thus beseen that any energy that is coupled through a slot will enter anauxiliary waveguide 146 and travel therealong until it is radiated fromthe open end of the guide 146. The amount of the energy that is coupledthrough any given slot and into an auxiliary waveguide is of course afunction of the current in the coil 112 immediately preceding the slot.

Each of the auxiliary waveguides are provided with individual phasecontrol means similar to those in the first embodiment. These phasecontrol means include a ferrite core 148 and a coil 150. Although thereis a separate coil 150 for each auxiliary Waveguide, only one is shownfor the sake of clarity. These coils 150' are connected to a commutator152 similar to or a part of the first commutator 138 by means of brushes154. The segments of the commutator 152 are in turn connected to acurrent source so that the coils 150 will be energized to predeterminedamounts. These coils will be excited in sequence at the same rateas thecoils 112. Thus they will be effective to control the direction of theradiated beam in planes containing the axis of the array and planesnormal thereto.

In order to employ the array 100, the energy is fed through thewaveguide 108 so as to produce traveling waves of energy in thewaveguides 1132. Simultaneously therewith the commutators will rotate ata speed corresponding to the rate at which the beam is to scan the area.This will cause the energy in the traveling wave to be coupled throughthe slots and into the auxiliary waveguides. The energy .will then beradiated into space from the ends of the auxiliary waveguides. This Willoccur in a sequence that will cause the beam to rotate at the same speedas the commutators 133 and 152. At the same time, the coils 15%? willvary the relative phases of the various radiations so as to cause thebeam to be scanned throughout a predetermined range of angles in planescontaining the axis of the array 106.

It may thus be seen that the beam may be scanned entirely throughout anygiven area. The only moving parts are the small commutators 138 and 152so that the scan rate may be extremely high.

What is claimed is:

1. In a device of the class described, the combination of waveguidingmeans for carrying electromagnetic energy therealong, a plurality ofradiation means disposed along said waveguiding means and adapted to becoupled thereto, said waveguiding means having electromagnetic energyapplied thereto in a mode that Will not excite said radiation means, aplurflity of mode shifting means spaced along said waveguiding means fortransforming said energy from one mode to another mode at a plurality ofpreselected points along said waveguiding means, and control meansoperatively interconnected with said mode shifting means for energizingonly preselected ones of said mode shifting means to transfer saidelectromagnetic energy from said first mode into said second mode so asto excite the radiation means subsequent thereto, said control meansbeing effective to energize preselected ones of said mode shifting meansfor transforming said electromagnetic energy back into the other of saidmodes.

2. In a device of the class described, the combination of waveguidingmeans for carrying a traveling wave of electromagnetic energy therealongin either of two modes, a plurality of radiation means spaced along saidWaveguiding means and adapted to be coupled to energy in a first mode,one end of said waveguiding means having electromagnetic energy appliedthereto that axially traverses said waveguiding means in a second modethat will not excite said radiation means, a separate mode shiftingmeans disposed anterior to each of said radiators, each of said modeshifting means being effective to change the mode of propagation of saidenergy in said waveguiding means posterior thereto into one of saidmodes, and control means associated with each of said mode shiftingmeans for independently actuating said mode shifting means to controlthe mode of said energy posterior to its associated means, said controlmeans being effective to independently cause only preselected ones ofsaid mode shifting means to transform said energy into said first modeto thereby excite said radiation means posterior thereto, said controlmeans being effective to independently cause other preselected ones ofsaid mode shifting means to transform said energy into said second modewhich will not excite said radiation means.

3. An antenna array comprising a waveguide for carrying electromagneticenergy therealong, a series of resonant apertures in one wall of saidwaveguide for radiating electromagnetic energy into space, "one end ofsaid waveguide having electromagnetic energy applied thereto in a modethat will normally not excite said apertures, separate mode shiftingmeans for each of said apertures disposed anterior thereto for changingthe propagation of said energy from one mode to another mode, means forenergizing one of said mode shifting means to cause said energy to betransformed into a mode that will excite the aperture immediatelyposterior thereto whereby it will radiate energy into space, and meansfor energizing another of said mode shifting means posterior to saidfirst energized mode shifting means to cause said energy to betransformed back into said first mode whereby said apertures posteriorthereto will not be excited by the energy in said waveguide.

4. An antenna array comprising a waveguide for carrying electromagneticenergy therealong, a plurality of radi ators disposed along saidwaveguide for radiating said energy into space, electromagnetic energybeing coupled into said waveguide in a mode that will not excite saidradiators, a ferrite element disposed in said waveguide whereby saidenergy will propagate therethrough, a separate inductive means disposedanterior to each of said radiators for creating a magnetic flux fieldwithin said ferrite element for causing the mode of said energy tochange, means for individually energizing one of said inductive meanswhereby the electromagnetic energy posterior thereto will be in a modethat will excite said radiators and cause radiations into spacetherefrom, and means for exciting a subsequent one of said inductivemeans whereby the energy pos erior thereto will again be in said firstmode whereby subsequent radiators will not be excited.

5. An antenna array comprising a plurality of parallel waveguides forcarrying electromagnetic energy therealong, a plurality of aperturesdisposed in one wall of each or" said Waveguides for radiatingelectromagnetic energy into space, electromagnetic energy being coupledinto each of said waveguides to form traveling Waves that are in modesthat Will not excite said apertures, at least one ferrite meanspositioned inside of each of said waveguides and disposed within saidelectromagnetic energy, separate coils disposed around said waveguidesanterior to each of said apertures, each of said coils being effectiveto create a magnetic field through said ferrite means for causing themode of said traveling Wave to change at that point, means forindividually energizing preselected ones of said coils whereby thetraveling Waves posterior thereto will be in modes that will excite saidapertures and cause electromagnetic radiations into space therefrom, andmeans for exciting subsequent ones of said coils for causing the modesof said traveling waves to be transformed hack into said first nrodeswhereby subsequent apertures will not be excited.

6. An antenna array comprising a waveguide arranged into a circle toform a cylindrical outer wall, one end of said waveguide havingelectromagnetic energy applied thereto, a plurality of apertures in theouter wall of said waveguide for radiating electromagnetic energyradially outwardly into space therefrom, said apertures being arrangedso that they are not normally coupled to a traveling wave propagatingthrough said waveguide in a given mode, mode shifting means for each ofsaid apertures disposed anterior to the aperture for changing the modeof said traveling wave to individually couple said apertures to saidtraveling wave whereby said energy will be radiated outwardly in apredetermined radial direction, a separate auxiliary waveguide sectionmounted on said Waveguide for each of said apertures, phase shiftermeans in each of said auxiliary waveguides, and means for individuallyactuating each of said phase shifter means in preselected combinations.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN A DEVICE OF THE CLASS DESCRIBED, THE COMBINATION OF WAVEGUIDINGMEANS FOR CARRYING ELECROMAGNETIC ENERGY THEREALONG, A PLURALITY OIFRADIATION MEANS DISPOSED ALONG SAID WAVEGUIDING MEANS AND ADAPTED TO BECOUPLED THERTO, SAID WAVEGUIDING MEANS HAVING ELECTROMAGNETIC ENERGYAPPLIED THERETO IN A MODE THAT WILL NOT EXCITE SAID RADIATION MEANS, APLURALITY OF MODE SHIFTING MEANS SPACED ALONG SAID WAVEGUIDING MEANS FORTRANSFORMING SAID ENERGY FROM ONE MODE TO ANOTHER MODE AT A PLURALITY OFPRESELECTED POINTS ALONG SAID WAVEGUIDING MEANS, AND CONTROL MEANSOPERATIVELY INTERCONNECTED WITH SAID MODE SHIFTING MEANS FOR ENERGIZINGONLY PRESELECTED ONES OF SAID MODE SHIFTING MEANS TO TRANSFER SAIDELECTROMAGNETIC ENERGY FROM SAID FIRST MODE INTO SAID SECOND MODE SO ASTO EXCITE THE RADIATION MEANS SUBSEQUENT THERETO, SAID CONTROL MEANSBEING EFFECTIVE TO ENERGIZE PRESELECTED ONES OF SAID MODE SHIFTING MEANSFOR TRANSFORMING SAID ELECTROMAGNETIC ENERGY BACK INTO THE OTHER OF SAIDMODES.